This invention relates to a spherical cured product of a polymer or polymer composition containing linear organopolysiloxane blocks and a method for its preparation.
Organopolysiloxane has wide applications in various forms such as oil, rubber or resin for its characteristic properties such as excellent heat resistance, cold resistance, weathering resistance, mold release characteristics, water repellency, electrical characteristics and flame retardancy. The field of its application has further been widened by its combined use with various organic or inorganic materials. Organopolysiloxane powder is one of such products. The organopolysiloxane powders heretofore known include, for example, a powder prepared by grinding silicone rubber, a methylpolysilsesquioxane powder, a polysiloxane powder consisting of CH.sub.3 SiO.sub.3/2 units and CH.sub.3 HSiO units, and a polysiloxane powder consisting of CH.sub.3 SiO.sub.3/2 units, CH.sub.3 HSiO units and SiO.sub.4/2 units (refer to U.S. Pat. No. 3,086,953). The powder prepared by grinding silicone rubber corresponds to a cured product of a polymer composition containing linear organopolysiloxane blocks. Heretofore, the powdering of silicone rubber has been done by grinding it at a normal temperature or after freezing with dry ice, or by processing it in a grinder. When these conventional methods are employed, however, not only their productivity is poor but it is difficult to obtain a powder of small enough particle diameters. Further, the silicone rubber powder thus produced is attended by such problems that it is amorphous in shape, is high in cohesiveness and poor in dispersibility, and is low in lubricity. Therefore, it has had no application to practical use. Methylpolysilsesquioxane powder, polysiloxane powder consisting of CH.sub.3 SiO.sub.3/2 units and CH.sub.3 SiO units, or polysiloxane powder consisting of CH.sub.3 SiO.sub.3/2 units, CH.sub.3 HSiO units and SiO.sub.4/2 units is prepared by hydrolyzing the corresponding chlorosilane or alkoxysilane and washing the hydrolyzate with water, then drying and grinding it, but the resulting powders are still attended by the same problems as in the case of the silicone rubber powder. Moreover, these products are attended by another problem that they contain no linear organopolysiloxane blocks so that when they are incorporated in an elastomeric substance, the resulting addition product will become too hard. Such being the case, these polysiloxane powders have had no particular applications other than being used as an oil absorbent or being added to mortar or gypsum with an intent to impart water repellency.
Besides these, the powder prepared by pulverizing a silicone resin and an organic filler together is also attended by similar problems (refer to Japanese Patent Laid Open No. 146434/1977).
In U.S. Pat. No. 4,370,160 there is disclosed a method in which a UV-curable organopolysiloxane composition is irradiated with ultraviolet ray while being dispersed in water or the like to produce a cured powder of organopolysiloxane. But, this method is troublesome and causes an increase of cost because it requires filtration, washing and drying.